Department of Chemistry , University of Utah , Salt Lake City , Utah 84112-0850 , United States.
J Am Chem Soc. 2019 Jul 17;141(28):11036-11049. doi: 10.1021/jacs.9b01847. Epub 2019 Jul 8.
The DNA repair gene is induced in cells or animal models experiencing oxidative or inflammatory stress along with oxidation of guanine (G) to 8-oxo-7,8-dihydroguanine (OG) in the genome. We hypothesize that a G-rich promoter element that is a potential G-quadruplex-forming sequence (PQS) in is a site for introduction of OG with epigenetic-like potential for gene regulation. Activation occurs when OG is formed in the PQS located near the transcription start site. Oxidative stress either introduced by TNFα or synthetically incorporated into precise locations focuses the base excision repair process to read and catalyze removal of OG via OG-glycosylase I (OGG1), yielding an abasic site (AP). Thermodynamic studies showed that AP destabilizes the duplex, enabling a structural transition of the sequence to a G-quadruplex (G4) fold that positions the AP in a loop facilitated by the PQS having five G runs in which the four unmodified runs adopt a stable G4. This presents AP to apurinic/apyrimidinic endonuclease 1 (APE1) that poorly cleaves the AP backbone in this context according to in vitro studies, allowing the protein to function as a trans activator of transcription. The proposal is supported by chemical studies in cellulo and in vitro. Activation of expression via the proposed mechanism allows cells to respond to mutagenic DNA damage removed by NEIL3 associated with oxidative or inflammatory stress. Lastly, inspection of many mammalian genomes identified conservation of the PQS, suggesting this sequence was favorably selected to function as a redox switch with OG as the epigenetic-like regulatory modification.
DNA 修复基因在经历氧化或炎症应激的细胞或动物模型中被诱导，同时基因组中的鸟嘌呤 (G) 氧化为 8-氧代-7,8-二氢鸟嘌呤 (OG)。我们假设，在 中，一个富含 G 的启动子元件是一个潜在的 G-四链体形成序列 (PQS)，是引入 OG 的位点，具有表观遗传样的基因调控潜力。当位于转录起始位点附近的 PQS 中形成 OG 时，就会发生激活。通过 TNFα 引入的氧化应激或通过精确位置的合成掺入，将碱基切除修复过程集中在读取和催化 OG 通过 OG-糖苷酶 I (OGG1) 的去除上，产生一个无碱基位点 (AP)。热力学研究表明，AP 使双链体不稳定，使序列发生结构转换为 G-四链体 (G4) 折叠，使 AP 位于由 PQS 形成的环中，PQS 中有五个 G 序列，其中四个未修饰的序列采用稳定的 G4。这将 AP 暴露于脱嘌呤/脱嘧啶内切酶 1 (APE1) 中，根据体外研究，APE1 在这种情况下很难切割 AP 骨架，从而使该蛋白能够作为转录的转激活因子发挥作用。该提议得到了细胞内和体外化学研究的支持。通过所提出的机制激活 表达，使细胞能够响应与氧化或炎症应激相关的由 NEIL3 去除的诱变 DNA 损伤。最后，对许多哺乳动物基因组的检查发现了 PQS 的保守性，这表明该序列被有利地选择作为具有 OG 作为表观遗传样调节修饰的氧化还原开关发挥作用。
